Furnaces intended for continuous heating, before rolling, of products such as billets or blooms, are often provided with walking beams. Part of the hearth is formed by fixed beams while the remaining part is constituted by walking beams which have a circular or rectangular movement pattern. The products rest alternately on the fixed beams and on the walking beams the movement of which ensures the progress of these products.
The beams of these furnaces may be hollow and cooled by circulation of water. They may also be made of refractory material, which reduces the heat consumption of the furnace by reducing heat losses.
In furnaces with refractory beams, the heating of the products is principally ensured by the radiation of the furnace on their upper face and on their lateral faces. Their lower face which is constantly in contact with the refractory hearth, is heated only by heat conduction coming from the other faces and, in most of the furnace, is at a temperature lower than that of the rest of the product.
This difference in temperature provokes a difference in expansion of the upper and lower faces of the product, which brings about a bending of the latter in the vertical plane. This bending is detrimental to the advance of the products on the hearth; in fact, the bent products tend to tip and then risk overlapping in the camber of the bend is greater than the interval which separates two successive products.
U.S. Pat. No. 1,400,367 describes a furnace comprising a hearth provided with slots in which are engaged walking beams separated by a fixed beam of width greater than that of the walking beams. Into the lateral walls of the slots open out flues conducting the combustion gases; the latter circulate about the mobile elements of the hearth and avoid passage of cold air through the slots. However, the combustion gases and the smoke leaving through slots which have a limited width cannot effectively heat the lower face of the products to avoid bending thereof. Moreover, the lateral walls of the slots and those of the walking beams are in contact with the smoke and dust that the gas contains; this is a drawback, being given the relative movement of the walls of the slots and of those of the beams.